1. Field of the Invention
The present invention relates to a method and apparatus for charging storage batteries in which the charging voltage is varied as a function of temperature.
2. Description of the Prior Art
Constant voltage charging methods are known and are particularly applicable to the charging of sealed or semi-sealed batteries having electrodes with thin sintered supports. These methods either use two voltage steps, one high and the other low, which are used respectively for main charging and for maintaining charge, or a single voltage step is used with automatic cut-out thereof. One such method is disclosed in U.S. Pat. No. 3,599,071, which is hereby incorporated herein by reference. In these known methods, when the temperature of the battery, TB, is less than or equal to the sum of the ambient temperature, TA, plus a first temperature difference, .DELTA.T1, charging takes place at the high voltage step. At or near termination of charging, however, the temperature of the battery rises and when it reaches and exceeds the ambient temperature TA plus a second temperature difference, .DELTA.T2, charging at the high rate is prevented. The values .DELTA.T1 and .DELTA.T2 can be, for example, respectively about 6.degree. C. and about 12.degree. C. The change-over from one voltage step to the other under the influence of temperature is immediate, i.e., the switching is substantially instantaneous. As long as the ambient temperature is less than 20.degree. C., the regulation thus obtained brings about a correct and reproducible stabilization of the charging current of a battery being charged at constant voltage at or near the termination of charging. The same does not apply above 20.degree. C., however, where the battery electromotive force varies to a great extent from battery to battery or even for a single battery at different periods in its life. The result of this is that the charging currents delivered when the high voltage is applied can be too low or too high. If they are too low, the battery does not terminate charging within the expected time; if they are too high, there is a danger of thermal runaway. The present invention obviates these prior art drawbacks and disadvantages and provides additional advantages which will be more apparent hereinafter.